JPH0217422B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a bottomed seamless paper molded container and its manufacturing method, and more particularly to a heat-resistant container whose contents can be heated and cooked using a microwave oven, an electric oven, a toaster oven, etc. . (Prior Art) Tray-shaped paper containers are widely used as containers that can be easily filled with food and other contents.
In recent years, with the spread of ovens, microwave ovens, toaster ovens, etc., cooked or uncooked foods are sold in tray-shaped containers, and when eating, the containers are placed in the above-mentioned heater and heated or heated. It is desired to develop a container that can be used for shoe packing. As a response to such requests, the special public
-41890 discloses that after paper stock is prepared at near neutrality, a base paper is made by infiltrating an aqueous dispersion containing an inorganic filler, and then a heat-resistant coating is attached or laminated on both sides of the base paper. , describes a method for manufacturing paper for food containers, which comprises applying a heat-resistant resin to the surface that will become the inside of the container. In addition to aluminum foil, resins such as nitrocellulose lacquer, epoxy, urethane, and fluorine are used as the heat-resistant coating. It is also described that heat-resistant resin such as silicone-based resin is applied. (Problem to be solved by the invention) Although this container can be used for filling raw materials such as Uiro, Castella, etc. and performing heat treatment at a temperature of about 200 to 250 degrees Celsius, it can be heated in a toaster oven, etc. Alternatively, when packing is performed, the temperature of the container reaches a high temperature of 300° C. or higher, and the heat resistance is not yet fully satisfactory for such high-temperature applications. Paper cellulose fibers begin to carbonize and become colored at a temperature of about 260°C, and are completely carbonized at a temperature of about 300°C. Thus, when paper containers are used for applications where they are hardened at temperatures of 300°C or higher, the appearance of the container itself becomes colored black to the extent that it cannot withstand use, and the strength of the container itself is also significantly lost. It is. In order to hide the coloring of paper containers, it is natural to consider providing a coating layer consisting of a hiding pigment and a resin binder on the surface of the paper substrate, but such coated paper generally has a high elongation required for molding. There is a difficulty in press moldability into a chipped tray, and when a press mold is heated to improve the moldability, the coating layer adheres closely to the mold and tends to cause defects that make molding impossible. In addition to this forming problem, conventional tray containers made of coated paper tend to emit bad odors when heated in ovens, and also have the disadvantage of impairing the flavor of foods. Therefore, the present invention provides a heat-resistant product that is composed of a paper laminate with excellent formability and has excellent appearance characteristics, container strength, and flavor retention even when the container wall is heated to a temperature of 300°C or higher. Our objective is to provide a paper container and its manufacturing method. (Means for Solving the Problems) The present inventors used a thermosetting resin as the resin when coating a paper substrate with a coating layer containing a resin and a hiding pigment. When applied in aqueous dispersion or water-soluble form, the seepage into the paper substrate that occurs when applying organic solution-based paints is prevented, and as a result the processability of paper laminates is significantly improved and the laminate It was also found that the body's heat resistance was significantly improved. According to the present invention, in a bottomed seamless molded container consisting of a paper substrate and a resin coat layer provided on at least one surface of the paper substrate, the resin coat layer has an epoxy resin component and a reactivity with respect to the epoxy resin. The resin coat layer has a thickness of the laminate L and a penetration depth from the surface of the coat layer into the paper substrate L. When
A seamless molded container with a bottom is provided, which is characterized in that it is provided so as to satisfy l/L<0.1. Further, according to the present invention, a heat-cured resin composition having an average particle size of 0.05 to 1.0 μm, which contains a hiding pigment as a dispersoid, and is composed of an epoxy resin component as a resin component and a curing agent resin component that is reactive with the epoxy resin. An aqueous dispersion containing a thermosetting resin is applied to at least one surface of a paper substrate, the applied layer is dried, the thermosetting resin is cured, and the resulting laminate is press-molded into the shape of a seamless container with a bottom. Provided is a method for producing a bottomed seamless paper container. The present invention further provides a method in which a water-based paint containing a hiding pigment as a dispersoid and a water-soluble thermosetting epoxy-acrylic resin as a resin component is applied to at least one surface of a paper substrate, and the applied layer is dried. death,
The present invention also relates to a method for manufacturing a seamless molded paper container with a bottom, which comprises curing a thermosetting resin and press-molding the resulting laminate into the shape of a seamless container with a bottom. (Function) In FIG. 1 showing a perspective view of the heat-resistant paper container of the present invention, this tray-shaped paper container has a rectangular and planar bottom wall portion 1 and a side wall portion 2 connected to the bottom wall portion 1.
a, 2b, 2c, and 2d, there are folds 3 between adjacent sidewalls, and a flange or curled portion 4 is provided on the upper edge of the sidewall. The second image shows an enlarged cross-sectional structure of the container wall of this paper container.
In the figure, this vessel wall 10 includes a paper substrate 11 and heat-resistant coating layers 12a and 12 applied to both surfaces of the paper substrate.
It consists of b. In the present invention, this heat-resistant coating layer 12a,
12b is formed from a hiding pigment and a thermosetting resin. First, the hiding pigment thermally isolates the paper substrate 11 from the heated high-temperature atmosphere, thereby maintaining the paper substrate's tendency to decrease in strength under heating to a small level, and also acts on the coating itself. It has the effect of imparting heat resistance and concealing fiber charcoal formed on the paper substrate to maintain a good appearance. Furthermore, the hiding pigment contained in the paint also has the auxiliary effect of somewhat reducing the formation and accumulation of resin stickies on the mold surface, thereby improving moldability. The hiding pigment is held to the paper substrate surface via a resin binder, which must be a thermosetting resin. First, these coatings 12a, 12
When a thermoplastic resin is used as b, it tends to cause molding problems such as the coating sticking to the mold when press-molding into a container, and it also generates bad odor, strange taste, and odor when heated in an oven, etc. Although there is a marked tendency for the flavor of foods to be impaired and the strength of the container itself to decrease, by using a thermosetting resin as the binder component, the above-mentioned disadvantages can be eliminated or alleviated. When forming the coating layers 12a and 12b, an aqueous dispersion containing a hiding pigment and a thermosetting resin with an average particle size of 0.05 to 1.0 μm is used as a dispersoid, or an aqueous dispersion containing a hiding pigment as a dispersoid and a water-soluble resin component as a resin component is used. The second feature is that a water-based paint containing a thermosetting epoxy-acrylic resin is used.
Conventionally, paints containing pigments and thermosetting resins are
Most often used as a solution in an organic solvent. However, as already pointed out, when applying an organic solution type paint to a paper substrate, it is unavoidable that the thermosetting resin penetrates deeply into the paper substrate. In contrast, in the present invention, the hiding pigment and the thermosetting resin are applied in the form of an aqueous dispersion, or the thermosetting resin is applied in a water-soluble form, so that the thermosetting resin permeates into the paper substrate. can be significantly reduced. That is, the thickness of the vessel wall (laminate) 10 is L, and the penetration depth from the surface of the resin coat layers 12a, 12b is l.
According to the present invention, l/L can be suppressed to less than 0.1, preferably within the range of 0.015 to 0.08. However, the penetration depth l may differ between the maximum depth and the minimum depth depending on the condition of the paper quality, but in this case, the average penetration depth should be l. By using aqueous dispersion type or water-soluble type resin in this way, the resin coat layers 12a, 12
Possible reasons why the penetration depth of b can be suppressed to a small value are as follows. That is, the paper substrate in the present invention uses a neutral sizing agent such as an alkyl ketene dimer or alkenyl succinic anhydride, or a rosin-based sizing agent with a weakly acidic formulation that has a reduced amount of sulfuric acid bands. Sizing treatment is performed to make paper water resistant, that is, to prevent water from seeping into the paper even if the surface of the paper gets wet. Therefore, when a water-based paint containing water as a medium is applied to a paper substrate as in the present invention, the degree of seepage of the resin into the paper substrate is significantly suppressed due to the effect of the sizing agent. Additionally, since paper generally absorbs water and organic solvents through the gaps between the fibers due to the hair thinning effect, if the resin is an aqueous dispersion larger than the gaps between the fibers, seepage of the resin into the paper base will be further suppressed. It will be done. On the other hand, when an organic solvent-based paint is used, the paint permeates deep into the paper substrate because the sizing agent does not have the effect of suppressing seepage of the organic solvent. Further, in the present invention, the resin coat layer 12a,
The reason why the moldability and heat resistance of the laminate are improved by suppressing the penetration depth of 12b to a small value is considered to be as follows. In other words, it is recognized that the press formability of paper laminates is due to the paper fibers being moderately intertwined or crossing each other in the paper substrate, and maintaining a moderate elongation. It is recognized that when the resin permeates deeply into the paper, the intertwined or intersecting parts become fixed and the elongation of the paper substrate is lost, resulting in a loss of press formability. On the other hand, in the laminate according to the present invention, the penetration depth of the thermosetting resin is extremely shallow, and the original elongation of the paper substrate is maintained, and as a result, it is thought that good press formability is maintained. In addition, by suppressing the permeation of the thermosetting resin into the paper substrate, a dense heat-blocking film is formed on the surface of the paper substrate.
It is recognized that the heat resistance of the laminate is improved. (Operations and Effects of the Invention) According to the present invention, a coating layer containing a hiding pigment and a thermosetting resin is provided on the surface of a paper substrate while suppressing permeation into the paper substrate. Even when the container wall is heated to a temperature of 300℃ or higher, it is possible to significantly improve the appearance characteristics, container strength, and flavor retention of the container, making it suitable for both microwave ovens and toaster ovens. A dual ovenable container that can be used for various purposes has been provided. (Description of Structure of the Invention) Thermosetting Resin The present invention uses a thermosetting resin consisting of an epoxy resin component and a curing agent resin component that is reactive with the epoxy resin. Suitable examples of hardener resin components include phenol formaldehyde resin,
Examples include urea formaldehyde resin, melamine formaldehyde resin, and acrylic resin. Among these, in the present invention, a combination of an epoxy resin and a reactive acrylic resin and/or vinyl resin having a functional group such as a carboxyl group, a hydroxyl group, or an amino group, such as a group reactive with the epoxy resin, is preferred. It is. These epoxy/acrylic or epoxy/vinyl coatings are particularly suitable for the purposes of the present invention in that they have excellent processability under crosslinked conditions and less stickiness formation on mold surfaces. . As an epoxy resin component, bisphenol A
Aromatic epoxy resins obtained by condensing epoxy and epihalohydrin are particularly suitable, and their epoxy equivalents are generally in the range of 1,000 to 4,000. As the acrylic resin, monomer components providing the functional groups include unsaturated carboxylic acids such as methacrylic acid, acrylic acid, and maleic anhydride, or their anhydrides; (meth)acrylic acid-2-hydroxyethyl ester, ( meth)acrylic acid-
Hydroxy group-containing monomers such as 2-hydroxypropyl ester; (meth)acrylic acid-2-aminoethyl ester, (meth)acrylic acid-2-N,
At least one type of amino group-containing substance such as N-diethylaminoethyl ester and (meth)acrylic acid-N-aminoethyl-aminoethyl ester;
Examples include copolymers containing at least one type of (meth)acrylic acid alkyl ester (for example, methyl methacrylate, ethyl acrylate, etc.) and, if desired, styrene. Vinyl resins include vinyl chloride-maleic anhydride copolymer, vinyl chloride-acrylic acid-acrylic ester copolymer, partially saponified vinyl chloride-vinyl acetate copolymer, vinyl chloride-styrene maleic anhydride, etc. Examples include carboxyl group- and/or hydroxyl group-containing vinyl resins such as polymers and saponified vinyl chloride-methacrylic acid-vinyl acetate copolymers. These resins have resin particles with a diameter of 0.05 to 1.0μ.
They are used in the form of aqueous dispersions, especially surfactant-emulsified or self-emulsified aqueous emulsions, as well as in water-soluble forms and in combinations thereof. Among these, for the purpose of the present invention, it is preferable to use epoxy-acrylic resins, particularly self-emulsifying epoxy-acrylic resins. Suitable examples of such epoxy-acrylic resins include 12 to 30% by weight of acrylic or methacrylic acid and styrene, methylstyrene, vinyltoluene or 1 carbon atom of acrylic or methacrylic acid.
an alkali-neutralized acrylic resin (A) having a number average molecular weight of 10,000 to 100,000, which is copolymerized with 70 to 88% by weight of one or more alkyl esters, and an average of 1.1 to 8 alkyl esters per molecule;
An aromatic epoxy resin (B) having a number average molecular weight of 1400 or more and having 2.0 epoxy groups is reacted with an epoxy resin with an excess of carboxyl groups and an acrylic resin partially reacted with the PH of the final coating composition. Examples include those dispersed in an aqueous medium in the presence of ammonia or amine in an amount of from 5 to 11. Further, there is also a water-soluble type by increasing the ratio of acrylic resin to epoxy resin, for example, 8:2 or 9:1, and adding a small amount of alcohol solvent. Furthermore, a combination of a water-soluble resin and an aqueous emulsion resin can also be used. Hiding Pigments Hiding pigments include non-toxic or low-toxicity pigments with high hiding power, especially those with good hiding power (JIS K5101).
No more than 40 pigments are used. Examples of suitable pigments are as follows.

[Table] These pigments may be used alone or in combination of two or more types, but the preferred pigment is one mainly composed of rutile type or anatase type titanium white (titanium dioxide). Of course, instead of using titanium white alone, for example, a small amount of yellow iron oxide, red iron oxide, or ultramarine may be blended to form a colored coating layer of cream color, pale pink, pale blue, or the like. Furthermore, fillers or extenders such as aluminum hydroxide, magnesium hydroxide, talc, clay, magnesium silicate, calcium silicate, etc. can be used for this pigment. Paper substrate Paper may be one or two of the following: natural pulp such as softwood pulp and hardwood pulp; inorganic fibers such as glass fiber, rock wool, slag wool, asbestos, and ceramic fiber; and synthetic resin pulp such as polyolefin, polyester, polyamide, and polyimide.
Examples include natural or synthetic paper obtained by paper-making more than one type of paper. These papers can be blended with fuel-retardant fillers, such as aluminum hydroxide, magnesium hydroxide, calcium aluminate, dawsonite, and the like. In addition, silica, talc, clay, calcium carbonate, etc. can be added to improve the texture and stiffness of the paper, and an organic resin binder can be added to improve paper formability and bond or fix fibers to each other. can be used. In the present invention, even when using ordinary paper obtained from wood pulp,
The advantage is that it can impart significantly better heat resistance. The basis weight of the paper substrate is 100 to 600 g/m ² , especially 150 g/m 2
It is desirable that the amount is in the range of 400 g/m ² to 400 g/m 2 . In terms of heat resistance, weakly acidic paper or neutral paper, particularly neutral paper using an alkyl ketene dimer, alkenyl succinic anhydride, etc. as a sizing agent, is particularly preferred. Manufacture of laminated material The laminated material used in the present invention is prepared by preparing an aqueous coating solution containing the above-mentioned thermosetting resin and hiding pigment, applying this coating solution to both sides of a paper substrate, and curing the formed coating. It can be obtained by Although the ratio of the thermosetting resin and the hiding pigment can be varied, the resin of the coating layer has the following formula R _P = k・O _A・d _R ... (1) where O _A is the oil absorbent of the hiding pigment. (ml/100g), d _R represents the density of the resin (g/ml), and k is a number from 0.005 to _0.2 . In this specification, the above formula (1) has the following meaning. O _A on the right side of equation (1) is the oil absorption amount of the concealing pigment (ml/100g), and the product of this and the resin density d _R is the homogeneous composition in which the resin is a continuous phase and the pigment is a dispersed phase. 100g of pigment to the extent that it can form
Means grams of binder per unit. Therefore, when this composition is applied to a smooth and impermeable substrate surface such as a glass plate, the value of k on the right side of equation (1) becomes
When the value of k is 0.01 or more, the pigment particles are not exposed on the outer surface, and a coat layer is formed inside without voids or irregularities near the surface, and when the value of k is less than 0.01, the pigment particles are exposed on the outer surface, or A coating layer with unevenness is formed inside as well in the voids and near the surface. At a pigment-to-resin weight ratio (R _P ) where the value of k in formula (1) is 0.2 or less, the pigment particles are exposed on the outer surface, or a coating layer with voids and unevenness is formed inside the pigment particles near the surface. A laminate having such a coating layer has the same elongation as a paper substrate and can be easily formed into a tray shape. The value of k in equation (1) has a certain minimum standard value in terms of the adhesion of the hiding pigment to the paper substrate, and if the value of k is less than 0.005, the separation of the hiding pigment during molding may occur. Moreover, the heat resistance strength of the vessel wall also decreases. The solid content concentration of the coating liquid is as low as possible within the range that provides uniform coating properties, and is generally suitably in the range of 20 to 80% by weight. Coating means such as spray coating, electrostatic coating, roller coating, gravure roll coating, dipping coating, and electrodeposition coating are used for coating. The coating amount on the paper substrate is 2 to 30% as solid content.
m ² /g, especially 5 to 20 m ² /g,
A satisfactory combination of heat resistance and processability is obtained. Curing of the coating formed takes place by means known per se, such as catalysis, heating or irradiation with ultraviolet light or radiation. Forming into a container Forming into a bottomed seamless container such as a tray, bowl, or cup is performed by heating a male mold and a female mold, supplying a laminated material between them, and press-forming. By heating the mold, the shaping of the laminated material is dramatically improved compared to when an unheated mold is used. The heating temperature of the mold is generally 50 to 50℃.
The temperature is preferably 180°C, particularly in the range of 90 to 150°C. The invention is illustrated by the following example. Example 1 First, a water-based epoxy-acrylic paint containing titanium white as a hiding pigment was prepared by the following procedure. (A) Production of carboxyl group-containing acrylic resin Styrene 300.0 parts Ethyl acrylate 210.0 Methacrylic acid 90.0 Ethylene glycol monobutyl ether
388.0 Benzoyl peroxide 12.0 Place 1/4 of the mixture with the above composition into a 4-necked flask purged with nitrogen gas, heat to 80-90°C, and while keeping it at that temperature, gradually add the remaining 3/4 over 2 hours. After dropping, continue at that temperature for 2 hours.
After stirring for an hour, it was cooled and the acid value was 93 (solid content equivalent).
(same below), solids content 59.7%, viscosity 4100cps (25℃,
A carboxyl group-containing resin solution was obtained (all viscosities below are measured at 25°C). (B) Production of epoxy resin solution Epicote 1007 500 parts ethylene glycol monobutyl ether
333.3 Pour the entire amount into a 4-necked flask purged with nitrogen gas, gradually heat to raise the internal temperature to 100℃, and
After stirring for a period of time until complete dissolution, the mixture was cooled to 80°C to obtain an epoxy resin solution with a solid content of 60%. (C) Preparation of aqueous coating resin composition 100.0 parts of the above (A) carboxyl group-containing acrylic resin solution 50.0 parts of the above (B) epoxy resin solution 2-dimethylaminoethanol 9.3 ion-exchanged water 290.7 Pour all of the above into a 4-necked flask. , was added with stirring to substantially neutralize the carboxyl groups contained in the cell, and then the internal temperature was raised to 80°C, stirring was continued at this temperature for 30 minutes, and then cooled to room temperature. The reduction rate of oxirane % was 63.5%, and the viscosity was also 1.5 times thicker after packing compared to before packing. To the thus obtained dispersion, rutile titanium oxide with an oil absorption of 20 and a specific gravity of 4.2 and ion-exchanged water were added in an amount equal to the solid content, and the total solid content of the resin and titanium oxide was adjusted to 50%. This mixture was kneaded using a ball mill type attritor to uniformly disperse titanium oxide. Next, this titanium white-containing water-based epoxy-acrylic paint was stretched to a height of 2.0%, a width of 6.0%, and a basis weight of 300.
g/ ^m2 , softwood pulp (NBKP) 30wt%, hardwood pulp (LBKP) 70wt% as chemical pulp
%, was coated with a bar coater on both sides of an acid-free paper substrate containing 5 wt % of talc as an inorganic filler and alkyl ketene dye as a sizing agent, and was dried and baked in an oven at 190°C for 1 minute. I went. The coating amount of the paint was 14 g/m ² on one side, and the coating amount of the hiding pigment was 7 g/m ² . FIG. 3 shows an enlarged photograph of the cross section of the thus obtained laminate using an optical microscope. When L and l were measured from this figure, L
is 380μm, l is 21.7μm at maximum value, 6.9μm at minimum value
m, the average value was 10.3 μm. Therefore, l/L
The maximum value is 0.057, the minimum value is 0.018, and the average value is
It was 0.027. Next, using a laminate coated with this titanium white-containing epoxy-acrylic paint on both sides, the temperature was adjusted after blanking and scoring.
By press molding with a press mold maintained at 140℃, the length is 16 cm as shown in Figure 1.
A square tray with a width of 9.5 cm and a depth of 2 cm was obtained. In this case, paint may adhere to the mold during molding, or
The molding was performed satisfactorily without any falling off, and without any cracks or cracks. Put 6 chicken nuggets in this square tray,
After storing it in the freezer for 2 days, it was heated in a toaster oven for 8 minutes. After heating, the tray was removed from the toaster oven and the chicken nuggets were found to be at an appropriate temperature and delicious. Further, at this time, the surface of the square tray was not burnt and no discoloration was observed. Examples 2 to 5, Comparative Examples 1 and 2 The coatings shown in Table 1 were applied to both sides of the paper substrate used in Example 1 using a bar coater so that the coating amount was 14 g/m ² of solids per side. Dry cured in an oven at 190°C for 1 minute. Figures 4 to 9 depict enlarged photographs of the cross sections of the various laminates thus obtained, taken using an optical microscope. From this figure, L and l
Table 1 shows the measured l/L values. Next, each laminate was blanked and ruled, and then a press mold kept at 140°C was used to form a shape of 16 cm long and 9.5 cm wide as shown in Figure 1.
It was molded into a square tray with a depth of 2.0 cm. Table 1 shows the press formability in this case, that is, the degree of paint adhesion to the mold, paint falling off, paint cracking, and laminate breakage. As is clear from Table 1, when an organic solvent-based paint was used, the l/L value increased, and there was a tendency for breakage or cracks to occur during molding.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a perspective view showing the heat-resistant paper container of the present invention, FIG. 2 is a cross-sectional structural diagram of the container wall of the paper container of the present invention, and FIG. 3 is a laminate of Example 1. It is a diagram depicting a micrograph showing the cross-sectional structure of the fourth
5, 6 and 7 are micrographs showing the cross-sectional structures of the laminates of Examples 2 to 5, respectively, and FIGS.
FIG. 2 is a diagram depicting a micrograph showing the cross-sectional structure of the laminate. Reference number 1 is the bottom wall part, 2a, 2b, 2c and 2
d is a side wall portion, 3 is a pleat portion, 4 is a flange portion or curl portion, 10 is a wall portion, 11 is a paper substrate, 12a, 1
2b indicates a heat-resistant coating layer.

Claims (1)

[Scope of Claims] 1. A bottomed seamless molded container comprising a paper substrate and a resin coat layer provided on at least one surface of the paper substrate, wherein the resin coat layer is reactive with an epoxy resin component and an epoxy resin. a thermosetting resin consisting of a curing agent resin component having the following properties and a concealing pigment;
When the resin coating layer has a thickness of the laminate as L, and a penetration depth from the surface of the coating layer into the paper substrate as l,
A seamless molded container with a bottom, characterized in that it is provided to satisfy l/L<0.1. 2. The molded container according to claim 1, wherein the paper substrate is low acid or neutral paper. 3. The molded container according to claim 1, wherein the hiding pigment is titanium dioxide. 4. An aqueous dispersion containing a concealing pigment as a dispersoid, and a thermosetting resin having an average particle size of 0.05 to 1.0 μm, which is composed of an epoxy resin component and a curing agent resin component reactive with the epoxy resin as a resin component. applying the resin to at least one surface of the paper substrate, drying the applied layer and curing the thermosetting resin;
A method for producing a bottomed seamless paper container, comprising press-molding the obtained laminate into a bottomed seamless container shape. 5. The method according to claim 5, wherein the aqueous dispersion of thermosetting resin is a curable epoxy-acrylic resin having self-emulsifying properties. 6. A water-based paint containing a hiding pigment as a dispersoid and a water-soluble thermosetting epoxy-acrylic resin as a resin component is applied to at least one surface of the paper substrate, the coated layer is dried, and a thermosetting coating is applied. 1. A method for producing a seamlessly molded paper container with a bottom, which comprises curing a resin and press-molding the obtained laminate into the shape of a seamless container with a bottom.